Patients with poor risk all: ages 1-9 with initial WBC> 50,000 or ages between 10 years and 21 years are eligible. All patients will receive BFM induction. A day 7 marrow classify subjects as either rapid early responders. Slow responders whose cells are CD19+ will be randomized to continue on BFM induction with and without the addition of immunotoxin (B43-PAP).